A major AIDS vaccine trial recently got underway in Thailand. But a group of prominent AIDS researchers says the experiment is a waste of money and human resources.

With 16-thousand Thai volunteers, the U-S-backed AIDS vaccine trial is expected to be the largest in history. Peggy Johnston directs the effort at the U-S National Institutes of Health. She says researchers will be testing a new strategy.

"The idea is to combine two vaccines to try to induce in volunteers kind-of a one-two punch."

The two-shot vaccine is designed to turn on two different parts of the human immune system. If it works, the first shot would trigger cells that hunt and kill HIV-infected cells. A separate shot would generate antibodies that neutralize the virus. Researchers hope the two approaches together will produce results that are greater than the sum of their parts.

The problem, as critics see it, is that neither shot seems to work very well on its own. The first shot has not looked promising in preliminary tests. The second shot has already failed a previous large-scale trial. Cornell University AIDS researcher John Moore says putting the two together doesn't add up.

"There is this argument that naught plus naught might equal one. Personally, I don't buy into it. The evidence that the two vaccine components work better together than apart is really very poor."

Mr. Moore and 21 other prominent AIDS researchers wrote a commentary in a recent issue of the journal "Science" criticizing the trial. An AIDS activist organization called Treatment Action Group is also critical of the medical trials. Executive director Mark Harrington says the vaccine isn't worth its one-hundred-nineteen-million-dollar price tag.

"The question many of us are asking is why are we putting so much resources into a really failed package of vaccine candidates when there (are) better products which are ready to move forward."

This trial will be the third attempt so far to develop an AIDS vaccine. Mr. Harrington and the authors of the commentary in "Science" say if this one fails, it will be harder to find volunteers for the next one.

But co-founder Bill Snow of the AIDS Vaccine Advocacy Coalition disagrees. He says that volunteers know what they're getting into.

"When they consent to be in a trial, they understand that it might not be the ultimate vaccine and they're willing to participate because they want to move science forward. And people learn a lot about vaccines and get enthusiastic about the process."

Peggy Johnston of the National Institutes of Health concedes that there are better, more promising vaccine candidates under development. But, she says it's hard to know when they'll be ready to test in people.

"Given the urgency of the epidemic, we don't want to sit back and wait until we have complete consensus that we have something that's perfect."

Ms. Johnston says even an imperfect vaccine would be an improvement over the current situation, where there is none.